Black is threatening to capture the white pawn on c4, and hold it with b7–b5. White can avoid this in a number of ways. About 80% of games continue 5.Bg5 or 5.e3: the former constitutes a sharp pawn sacrifice, while the latter restricts the dark-squared bishop from its natural development to g5. Other possible moves are 5.Qb3, 5.g3 and 5.cxd5, the last of which, after 5...exd5, leads to a line of the QGD Exchange Variation where White's early Nf3 enables Black's queen bishop to freely develop, which should give equality (ECO codes D43 and D45).

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The main line continues with 5...Nbd7. The bishop moves 5...Bd6 and 5...Be7 are seldom seen, as masters realized early on that at e7, the bishop was passively placed and does nothing to further one of Black's aims, the freeing move ...e5. The unusual move 5...a6 is considered solid for Black. Some sources call 5...a6 the "accelerated Meran".[1]

The main variation of the Semi-Slav is the Meran Variation, 6... dxc4 7. Bxc4 b5 (ECO codes D46 to D49), when play usually continues with 8.Bd3, with 8.Be2 and 8.Bb3 less common alternatives. The line was first played in 1906 in the game Schlechter–Perlis.[2] The variation takes its name from the town of Meran (Merano) in northern Italy. During a 1924 tournament in Meran, it was used successfully in the game Gruenfeld–Rubinstein. Gruenfeld adopted the same variation two rounds later against Spielmann, winning as well.[3] Black surrenders his outpost on d5, gaining a tempo for queensidespace expansion by b7–b5. White will play in the center, leading to a rich, complicated game. These opposing strategies, with the ensuing keen play, have long made the Meran a favorite for enterprising players of either color. An example is Gligoric v Ljubojevic, Belgrade, 1979.[4]

After the move 8.Bd3, Black usually plays 8...a6. Bent Larsen introduced the move 8...Bb7, which has been dubbed the "improved Meran".[5] According to one source, the move was first played in 1923, but since it was developed by Larsen, it carries his name. Black can also play 8...Bd6, which is the move Anand played in his victory over Levon Aronian in the Tata Steel Chess Tournament 2013.[6]

Though appearing in contemporary master play with less frequency than the Meran, there are other possibilities: 6...Be7, 6...Bb4, introduced by the Italian master Max Romih, and 6...Bd6, which was much the most popular line before the debut of the Meran, and espoused by the American grandmasterArthur Bisguier throughout his career.

6...Bd6 and now 7. 0-0 0-0 8. e4 dxe4 9. Nxe4 Nxe4 10. Bxe4 is the most common line. There are now several alternatives for Black, with one a clear error, as it loses a pawn: 10... e5 11. dxe5 Nxe5 12. Nxe5 Bxe5 13. Bxh7+ Kxh7 14. Qh5+ Kg8 15. Qxe5. This line, however, has a strong drawish tendency in practice, due to the opposite-colored bishops, although all the heavy pieces remain on the board.

Black's other choices include 10...c5, although theory regards this as premature as it enables White to play for a kingside attack with 11.Bc2, followed by Qd3 and Bg5. 10...Nf6 has also been played, but this misplaces the knight and does nothing to further Black's play against the center by means of the pawn breaks c6–c5 or e6–e5. Bisguier preferred 10...h6 and it has come to be considered the strongest plan.

The other ideas, 6...Be7, which has the same drawback as after 5.e3 Be7, and 6...Bb4, have become sidelines in modern play.

The main alternative to 6.Bd3 has become 6.Qc2, once a sideline, this move exploded in popularity in the 1990s, in large part due to Anatoly Karpov's advocacy. The idea is to wait for Black to commit to ...dxc4 before playing Bd3. Black commonly replies with 6...Bd6 and now White can choose between two very different continuations:

The Anti-Meran Gambit (ECO code D44) arises after 5.Bg5. Possible replies include 5...Nbd7, 5...dxc4, 5...h6, and 5...Be7. White refuses to shut in the dark-squared bishop, instead developing it to an active square where it pins the black knight. It is now possible for Black to transpose to either the Cambridge Springs Defence with 5... Nbd7 6. e3 Qa5, or enter the Orthodox Defense with 6...Be7.

This line is extremely complicated, with theory stretching past move thirty in some variations. Black captures a pawn by 5...dxc4. White takes control of the center with 6.e4 as Black defends with 6...b5. The main line of the Botvinnik now continues 7. e5 h6 8. Bh4 g5 9. Nxg5 hxg5 10. Bxg5 Nbd7. White will regain his piece with interest, emerging with an extra pawn, but Black will soon complete his development, gaining great dynamic compensation, whereas White's task is rather more difficult. White will fianchetto his king bishop and castlekingside, while Black will play c5, Qb6, castle queenside, and can carry out an attack in the center or on either flank, leading to complex play. The opening was introduced by Mikhail Botvinnik in the 1945 USSR vs USA radio match vs Arnold Denker. Today, Alex Yermolinsky has an excellent record with the white pieces and Alexei Shirov has been Black's chief proponent in this variation. Although this variation bears Botvinnik's name, he was not the first person known to have played it—Klaus Junge is credited as the actual inventor.[8]

The Moscow Variation 5... h6 6. Bxf6 Qxf6 gives rise to play of a different character from the Botvinnik variation. Black has the bishop pair, which gives him good long-term chances, but must avoid prematurely opening the position in the face of White's superior development and central control, as his position is initially solid but passive. Alexei Dreev has played this line successfully as Black. The gambit line 6.Bh4 (the Anti-Moscow Variation) was once considered dubious, but has seen a recent resurgence. In return for the pawn, White receives a lead in development and a strong initiative. This dynamic line, which is characteristic of the modern game, has been played by many strong grandmasters, with the theoretical verdict remaining inconclusive.